A myriad of different types of pumps are known for use in pumping various materials. When it is desired to pump difficult materials, i.e., those that are highly viscous and/or abrasive, the number of choices of pumps suitable for such applications drops substantially, particularly when it is desired to pump such materials at relatively elevated pressures and/or at predetermined flow rates. While reciprocating piston pumps have been widely used in such applications, such pumps suffer from having pulses in the pressure output of the pumps during piston reversal. Such pumps also suffer to a certain extent from leakage and seepage of pumped material past the seals which is particularly critical when the material is air-sensitive such as isocyanates. This leakage is in both directions and can cause environmental contamination, pumped fluid contamination and regenerative abrasive wear damage to the pump. The reduction and/or elimination of pulses in the output is particularly important for circulating systems, fine spray applications and proportional metering to produce constant output.
Centrifugal pumps are capable of pumping abrasive materials without pressure pulses but suffer from the problems of not being positive displacement type (flow rate is not directly related to speed), inefficiency, shaft seal leakage and impose a high degree of shear on materials which may be shear-sensitive.
Gear pumps are commonly used for metering and proportioning apparatus due their ease in synchronizing with other pumps. Such products, however, are ill-suited for pumping of abrasive materials which cause unacceptable wear.
It is therefore an object of this invention to provide a pump capable of handling such materials while providing substantially pulseless operation. It is further an object of this invention to provide such a pump which is easily manufactured and which is capable of being operated at varying speeds, flow rates and pressures in an efficient manner. It is yet a further object of this invention to provide such a pump which has leak-proof operation to avoid contamination of the environment in which the pump is located or contamination of the pumped fluid by the environment.